A number of different methods of increasing the capacity of existing optical fibres in a network are known to the art. One method is to use wavelength division multiplexing (WDM) to improve the extent to which available bandwidths can be utilized on the optical fibre in the optical network. However, this technique requires the provision of means that can multiplex and demultiplex transmission channels that lay on different so-called optical carrier wavelengths in the optical network.
One type of multiplexing of particular interest with regard to so-called bus networks or ring networks is add/drop multiplexing, i.e. a process in which one or more so-called information channels disposed on the aforesaid carrier wavelengths are dropped from or added to an information flow.